JPH09297234A - Optical reflection end, production for optical reflection end and optical interference device using the optical reflection end - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a reflection end face whose relative position is correct by providing an optical reflection end at an end face to be faced with the channel waveguide of the slab waveguide optically connected to the end part of the channel waveguide. SOLUTION: A slab waveguide 2 is arranged at the terminal of a channel waveguide 1 and a reflection end is formed in the slab waveguide 2. That is, an optical waveguide consisting of the channel waveguide 1 and a clad 3 is formed on a silicon substrate 5 and the slab waveguide 2 is arranged at the terminal of the channel waveguide 1 and also an optical reflection film 4 of a metallic thin film or the like is arranged on the slab waveguide 2 to constitute a reflection end. Since the waveguide is the slab waveguide 2 in a reflection end boundary part and there is uniformity in a boundary line direction, ruggednesses and protrusions on the reflection end are never generated in a process transferring a pattern becoming the reflection end by a light exposure and in a process disclosing a reflection end face by a reactive ion-etching technology.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light reflecting end, a method for manufacturing the light reflecting end, and an optical interferometer using the light reflecting end.
More specifically, the present invention relates to a light reflecting end used in a single mode optical waveguide, and more specifically, to a light reflecting end having a high relative positional accuracy, which is manufactured in plural on the same substrate.

[0002]

2. Description of the Related Art A single mode optical waveguide manufactured on a flat substrate, especially a silica glass single mode optical waveguide which can be manufactured on a silicon substrate, has excellent compatibility with an optical fiber and is practical. It is expected as a means of realizing a waveguide type optical component. In particular, a waveguide type optical interferometer configured by this optical waveguide is expected as an important optical component such as an optical wavelength filter used for optical communication.

A waveguide type optical interferometer, for example, in a two-beam interferometer, is connected to a waveguide with a light reflection end having a desired difference in waveguide length as shown in FIG. 3 and these waveguides. There is known a reflection type optical interferometer, so-called Michelson type interferometer, which is composed of a combination of directional couplers. In addition to this, a transmission type optical interferometer, a so-called Mach, which is composed of a combination of two directional couplers and two optical waveguides in which the directional couplers are connected to each other with a desired difference in waveguide length. There is a Zender type interferometer.

From the viewpoint of making the circuit size compact, the reflection type optical interferometer is more advantageous for the reason described later. In order to provide the desired optical path length difference between the two waveguides that cause the interference operation, the transmission type optical interferometer uses the difference in the waveguide length due to the combination of the curved waveguide and the linear waveguide, and The optical interferometer is provided with a difference in the position of the light reflection end. Since the loss increases in the curved waveguide when the bending radius is reduced, there is a limit in reducing the bending radius.

For example, in a waveguide having a relative refractive index difference of 0.75%, this minimum bending radius is 5 mm, and in two waveguides giving an optical path length difference, even if the waveguide length difference is as small as 1 mm, 12 A waveguide of about 0.5 mm is required to secure this waveguide length difference. There is no such restriction on the position of the light reflection end. As described above, the waveguide type optical interferometer has a drawback that the circuit size is larger than that of the transmission type optical interferometer.

In the reflection type optical interferometer, the interference characteristic is determined by the difference in the distance between the two waveguides connected from the directional coupler to the light reflecting end, so that the position of the light reflecting end can be positioned with high accuracy. Fabrication becomes important. Further, in order to increase the reflectance at the light reflecting end, it is desirable that the reflecting surface be a plane and perpendicular to the waveguide.

FIGS. 4A, 4B and 4C show the structure of a conventional light reflecting end. 4 (a) is a plan view, FIG. 4 (b),
(C) is sectional drawing which followed the GG 'line and the HH' line, respectively. As shown in FIG. 4, a single mode buried optical waveguide composed of a channel waveguide core 1 and a clad 3 is formed on a silicon substrate 5, and a metal thin film or the like is formed on the end face of the waveguide exposed by a fine processing technique. The light reflection film 4 is arranged to form a reflection end. Further, FIG. 4D is a plan view of the waveguide arrangement before exposing the waveguide surface, and the reflection end is formed at the reflection end formation position 7 thereafter.

Such a reflection end is manufactured by the method described below, for example, in the above-mentioned silica glass single mode optical waveguide. First, as shown in FIG. 5B, the channel waveguide core 1 and the cladding are formed on the silicon substrate 5 shown in FIG. 5A by a known combination of the flame hydrolysis reaction deposition technique and the reactive ion etching technique. A single mode buried optical waveguide consisting of 3 is formed.

At this time, the buried waveguide is usually formed in FIG. 4 in consideration of the absolute positional deviation at the time of forming the light reflection end.
As shown in (d), it is made sufficiently longer than the light reflection end forming position. Next, as shown in FIG. 5 (c), a photoresist 6 is applied to the surface of the clad glass, and the photoresist 6 is applied thereon.
As shown in (d), the pattern to be the light reflection end is transferred by exposure.

Subsequently, as shown in FIG. 5 (e), an unnecessary portion including a waveguide, which is additionally formed outside the light reflection end, is removed by a reactive ion etching technique using this as a mask, and the end face of the waveguide is removed. Expose. Further, FIG.
As shown in (f), the light reflection film 4 made of a metal thin film or the like is formed on the end face of the waveguide by a vacuum evaporation technique.

[0011]

However, when the light reflecting end is manufactured by the above method, there are the following problems. That is, in the exposure process, the waveguide core 1
In the portion where is disposed, the resist exposure amount of the upper portion on the waveguide core side is slightly larger than that on the cladding side due to the lens effect of the core 1.

Therefore, when the waveguide core 1 is vertically arranged at the pattern boundary portion at the light reflection end, the exposure intensity in the direction along the boundary line also changes in the vicinity of the pattern boundary portion.
As a result, the boundary line between the resist of the exposed portion and the resist of the non-exposed portion becomes slightly concave in the portion above the waveguide core when viewed from the light-shielding pattern side when a positive resist is used.

Further, in the etching step, since the glass of the core portion and the glass of the cladding portion have different glass components, the etching rate is slightly different, and the etching surface is displaced. This also causes the road to have a slight protrusion on the end face of the core. Further, in the case of a waveguide having a thin clad glass for embedding, there is undulation that reflects the shape of the core embedded in the glass surface, and this also causes a slight protrusion on the end face in the vicinity of the waveguide core.

Since the sizes of the unevenness and the protrusions are slightly different depending on the individual waveguide cores as described above, when the light reflecting end is formed by using this end face, the relative position of the reflecting end. There is a deviation, and it is difficult to manufacture an optical interferometer having an accurate optical path length difference as designed.

The present invention has been made in view of the above-mentioned prior art, and in order to manufacture a waveguide type optical interferometer having desired characteristics, it is necessary to form a reflecting end face whose relative position is accurate. The purpose is.

[0016]

The light reflecting end according to claim 1 of the present invention which achieves such an object is provided in the vicinity of a channel waveguide on a substrate, and a light propagating through the channel waveguide is provided. The slab waveguide is a light reflecting end that reflects light, and is provided on an end face of the slab waveguide that is optically connected to the end of the channel waveguide and that faces the channel waveguide.

The light reflecting end according to claim 2 of the present invention which achieves the above object is a light reflecting end which is provided in the vicinity of the channel waveguide on the substrate and reflects the light propagating through the channel waveguide. The channel waveguide is provided on an extension of the channel waveguide so as to be separated from the channel waveguide, and a clad layer of the channel waveguide is interposed in a gap between the channel waveguide and the channel waveguide.

A method of manufacturing a light reflecting end according to a third aspect of the present invention which achieves the above object, comprises: exposing a photoresist coated on a surface of a slab waveguide connected to a channel waveguide on a substrate to a reflecting end by exposure. And a step of exposing the end face of the slab waveguide by removing unnecessary portions of the slab waveguide by using the pattern as a mask.
And a step of forming a light reflecting film on the end face of the slab waveguide.

According to a fourth aspect of the present invention which achieves the above object, a method of manufacturing a light reflecting end is characterized in that a photoresist coated on the surface of a region of only a clad layer connected to a channel waveguide on a substrate is reflected by exposure. And a step of exposing a clad end surface by removing unnecessary portions of the region by using the pattern as a mask, and a step of forming a light reflection film on the clad end surface. To do.

An optical interferometer using a light reflecting end according to a fifth aspect of the present invention which achieves the above object, comprises a plurality of waveguides with light reflecting ends each having a different waveguide length, and these waveguides are connected. In a reflection-type optical interferometer including a combination of optical couplers, the reflection end according to claim 1 or 2 is used as the reflection end.

[0021] Claims 6 and 7 of the present invention which achieve the above object.
An optical interferometer using a light reflecting end according to claim 5 is characterized in that a directional coupler is used as the optical coupler according to claim 5 or a slab waveguide is used.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The light reflecting end of the present invention does not have a reflecting film formed at the end of the channel waveguide 1,
The slab waveguide 2 or the region 3 having only the cladding layer is provided at the end of the channel waveguide 1, and the reflection end is formed in the region 3 having only the slab waveguide 2 or the cladding layer.

Therefore, there is no change in the structure of the core waveguide or the like in the boundary line direction in the vicinity of the pattern boundary, and the pattern is uniform in the boundary line direction. No unevenness or protrusion is formed on the end face of the waveguide core.

Therefore, in the optical interferometer using this light reflecting end, it is possible to provide a highly accurate optical path length difference, so that it is possible to reduce variations in the transmission center wavelength and crosstalk.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. The following example is an example applied to a light reflecting end using a silica-based single mode optical waveguide formed on a silicon substrate as an optical waveguide. This is because this combination excels in connection with a single-mode optical waveguide. However, the present invention is not limited to these combinations.

[Embodiment 1] FIGS. 1A, 1B, 1C and 1D show the structure of a light reflecting end according to a first embodiment of the present invention.
Shown in FIG. 1 (a) is a plan view, FIG. 1 (b), (c),
(D) is sectional drawing along AA ', BB', and CC ', respectively. FIG. 1E is a plan view of the waveguide arrangement before exposing the ends of the waveguide.

In this embodiment, the reflection film is not formed at the end of the channel waveguide 1, but the slab waveguide 2 is arranged at the end of the channel waveguide 1, and the reflection end is provided at this slab waveguide 2. It was formed.

That is, an optical waveguide consisting of the channel waveguide core 1 and the cladding 3 is formed on the silicon substrate 5, and the slab waveguide 2 is formed at the end of the channel waveguide 1.
And a light reflection film 4 such as a metal thin film is arranged on the slab waveguide 2 to form a reflection end.

In the present embodiment, the waveguide is the slab waveguide 2 at the boundary portion of the reflection end, and since there is uniformity in the direction of the boundary line, exposure is performed as shown in FIGS. In the process of transferring the pattern to be the reflection end or by the process of exposing the reflection end face by the reactive ion etching technique, the unevenness or protrusion on the reflection end face as described in the prior art did not occur. As shown in FIG. 1E, a reflective end is subsequently formed at the reflective end forming position 7.

Further, in the embodiment described later, the waveguide structure immediately before the reflection end has no core, but the waveguide structure of this embodiment is the slab waveguide 2 and the silicon substrate 5 Since the light is confined in the vertical direction, the structure without a core is advantageous in terms of loss.

[Embodiment 2] FIG. 3 shows a reflection type two-beam interferometer according to a second embodiment of the present invention. The reflective two-beam interferometer of this embodiment uses the light reflecting end shown in FIG. In the reflection-type two-beam interferometer of this embodiment, the silica-based optical waveguides 21a, 21b, 23a, and 23b are manufactured on the silicon substrate 5 having a diameter of 4 inches by the combination of the flame deposition technique and the reactive ion etching technique as in the conventional case. Then, the reflection film is formed at a desired position by the vacuum vapor deposition method and chemical etching.

The cross-sectional dimension of the core is 6 μm square, and the relative refractive index difference between the core and the clad is 0.75%. Al was used for the reflective film. The length of the slab waveguide in the waveguide direction is 5
μm. Further, the difference ΔL in the substantial length of the delay line waveguides 23a and 23b from the directional coupler 22 to the reflection end structure portions 24a and 24b is set to 828 μm. Input waveguide 2
Wavelength interval (FS) of light passing from 1a to the output waveguide 21b
R) Δλ is represented by Δλ = λ ² / 2nΔL, and the transmission wavelength to the output waveguide 21b is λ = 2nΔL / m (m: integer).
It is.

Where n is the effective refractive index of the waveguide,
In the waveguide used this time, it is 1.451. Therefore, from this equation, the wavelength interval of the circuit this time is 1 nm, and for example, light of 1550.23 nm is transmitted to the output waveguide 21b.

When a similar reflection-type two-beam interferometer was manufactured using the light reflecting end according to the prior art, the center wavelength of the transmitted light had a variation of about 0.2 nm. Almost no variation in the center wavelength of light was observed, which was 1/10 or less of that of the conventional one, and a stable value was obtained. The excessive loss due to the insertion of the slab waveguide having a length of 5 μm in the waveguiding direction was as small as 0.1 dB.

[Embodiment 3] FIGS. 2 (a), 2 (b), 2 (c) and 2 (d) show the structure of the light reflecting end according to the third embodiment of the present invention.
Shown in 2 (a) is a plan view, FIG. 2 (b), (c),
(D) is sectional drawing along AA ', BB', and CC ', respectively. FIG. 2E is a plan view of the waveguide arrangement before exposing the ends of the waveguide.

In this embodiment, the reflection film is not formed at the end of the channel waveguide 1, but the region 3 of only the clad layer without the core layer is provided at the end of the channel waveguide 1, and only this clad layer is provided. The reflective end is formed in the region 3 of FIG.

That is, an optical waveguide consisting of the channel waveguide core 1 and the cladding 3 is formed on the silicon substrate 5, and the region 3 of only the cladding layer without the core layer is arranged at the end of the channel waveguide 1. At the same time, a light reflection film 4 such as a metal thin film is arranged in the region 3 having only the cladding layer to form a reflection end.

Also in this embodiment, as in the first embodiment described above, the waveguide is the slab waveguide 2 at the reflection end boundary portion.
Since there is uniformity in the direction of the boundary,
As shown in (f), in the process of transferring the pattern to be the reflection end by exposure and the process of exposing the reflection end face by the reactive ion etching technique, the unevenness or protrusions on the reflection end face as described in the prior art are generated. There wasn't. Incidentally, FIG.
As shown in (e), a reflection end is then formed at the reflection end formation position 7.

Further, as compared with the first embodiment described above, the waveguide structure immediately before the reflection end has no core, and there is no confinement of light in the direction perpendicular to the substrate 5, so that the slab waveguide is used. It is disadvantageous in terms of loss as compared with the structure using.

[Embodiment 4] FIG. 3 shows a reflection type two-beam interferometer according to a fourth embodiment of the present invention. The reflection type two-beam interferometer of this embodiment uses the light reflection end shown in FIG. The circuit specifications of the reflection-type two-beam interferometer of this embodiment are the same as those of the second embodiment described above, except that the distance between the core waveguide end and the waveguide of the reflecting surface is 5 μm.

Also in the reflection-type two-beam interferometer of this embodiment, there was almost no variation in the center wavelength of the transmitted light, which was one-tenth or less that of the conventional one, and a stable value was obtained.
The excessive loss due to the inclusion of 5 μm in the region 3 having only the clad layer without the core layer was as small as 0.3 dB.

[Embodiment 5] FIG. 6 shows the structure of a multi-beam interferometer to which a light reflecting end according to a fifth embodiment of the present invention is applied.
FIG. 6 is a plan view. The multi-beam interferometer of this embodiment is also called a reflection-type array waveguide grating multiplexer / demultiplexer, and has a plurality of input / output waveguides 31, slab waveguides 32, array waveguides 33 having different optical path lengths, and reflection ends. 34 are connected in order.

The light incident from any one input / output waveguide 31 is distributed to the arrayed waveguide 33 by the slab waveguide 32. The distributed light is reflected by the light reflecting end 34, undergoes a desired delay in the arrayed waveguide 33, and returns to the slab waveguide 32 again. The returned light is slab waveguide 3
2 causes a desired interference and is condensed on a desired input / output waveguide 31 according to the wavelength of the light, so that the light is input into the plurality of input / output waveguides 3
It is demultiplexed to 1. As described above, in the present embodiment, the point where a large number of light beams interfere with each other and are demultiplexed into a plurality of wavelengths is
Different from the fourth embodiment.

The deviation of the waveguide length difference was shown as a deviation of the central wavelength of the transmitted light (pass band) in the two-beam interferometers shown in the second and fourth embodiments, but the multi-beam interference. In addition to this, in the total, the optical output level rises in the stop band, that is, the stroke deteriorates. For this reason, the multi-beam interferometer is required to be more strict in the accuracy of the optical path length difference.

The specifications of the light reflecting end applied to the reflective multi-beam interferometer of this embodiment are the same as those of the first embodiment. The 64 arrayed waveguides 33 each have a waveguide length difference of 64.7 μm. The collected light is 100 GHz and 16
It was designed to be demultiplexed into the book input / output waveguide 31.

The circuit size was 30 mm × 10 mm. This is about one-third in area ratio as compared with the circuit size of the transmissive arrayed-waveguide grating multiplexer / demultiplexer of 26 mm × 40 mm, and a compact circuit, which is a characteristic of the reflective type, was realized. When a similar reflection-type multi-beam interferometer was manufactured using the reflection end according to the conventional technique, the optical output level (crosstalk) in the stop band was about −12 dB, and no decent characteristic was obtained. .

In this example, the optical output level (crosstalk) in the stop band was -30 dB, showing a considerable improvement in characteristics. This is because the relative positions of the light reflecting ends of the waveguides of the arrayed waveguides are created with high accuracy. The light reflection end according to the third embodiment described above can also be applied to the reflection-type multi-beam interferometer of this embodiment, and a region of only the clad layer without the core layer at that time is 5 μm. The excessive loss due to was 0.1 dB, which was small.

The length of the slab waveguide 2 in the first and third embodiments in the waveguide direction of the region 3 of only the cladding layer and the distance between the end of the core waveguide and the waveguide of the reflecting surface in the fifth embodiment. Is preferable from the viewpoint of loss, but
If the length is extremely short, the influence of the channel waveguide core 1 will occur. Therefore, it is desirable to finally take these into consideration when making a decision.

Further, in the above-mentioned embodiment, the example using the light reflecting end based on silica glass on the silicon substrate is explained, but other materials which can constitute the waveguide type optical interferometer,
For example, plastic optical waveguide or ion diffusion type waveguide,
Furthermore, it is additionally noted that the present invention can be applied to a lithium niobate-based waveguide and the like. Needless to say, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

[0050]

As described above in detail with reference to the embodiments, the present invention can provide a light reflecting end having excellent relative positional accuracy. Therefore, the light reflecting end can be used for reflection. When a type optical interferometer is created, compared to a reflection type optical interferometer using a light reflecting end with a conventional structure, it is possible to provide a highly accurate optical path length difference, reduce variations in transmission center wavelength, and crosstalk. Was able to be reduced. In particular, the present invention is extremely effective in realizing a reflection type optical interferometer using a waveguide, which can reduce the circuit size.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a structure of a light reflecting end according to a first embodiment of the present invention.

FIG. 2 is an explanatory view showing a structure of a light reflecting end according to a third embodiment of the present invention.

FIG. 3 is an explanatory diagram showing the structure of a reflective two-beam interferometer (Michelson interferometer) according to second and fourth embodiments of the present invention.

FIG. 4 is an explanatory view showing a structure of a conventional light reflecting end.

FIG. 5 is a process chart showing a process of forming a conventional light reflection end.

FIG. 6 is an explanatory diagram showing a reflection type multi-beam interferometer (reflection type arrayed waveguide grating).

[Explanation of symbols]

 1 Channel Waveguide Core 2 Slab Waveguide Core 3 Clad 4 Light Reflecting Film 5 Silicon Substrate 6 Photoresist 7 Reflection Edge Forming Position 21a Input Waveguide 21b Output Waveguide 22 Directional Coupler 23a, 23b Delay Line Waveguide 24a, 24b Reflection edge structure 31 Input / output waveguide 32 Slab waveguide 33 Arrayed waveguide (delay line waveguide) 34 Reflection edge structure

Front page continuation (72) Inventor Kuninori Hattori 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Fanta Suzuki 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation

Claims (7)

[Claims] 1. A light-reflecting end that is provided in the vicinity of a channel waveguide on a substrate and that reflects light propagating through the channel waveguide, and is optically connected to an end of the channel waveguide. A light reflecting end provided on an end face of the slab waveguide facing the channel waveguide. 2. A light reflecting end provided on the substrate in the vicinity of the channel waveguide and for reflecting light propagating through the channel waveguide, the light reflecting end being separated from the channel waveguide on an extension line of the channel waveguide. And a clad layer of the channel waveguide is provided in a gap with the channel waveguide. 3. A step of transferring a pattern to be a reflection end by exposure onto a photoresist applied to a surface of a slab waveguide connected to a channel waveguide on a substrate, and using the pattern as a mask, the slab waveguide is unnecessary. A method for manufacturing a light reflecting end, comprising: a step of removing a portion to expose an end surface of the slab waveguide; and a step of forming a light reflecting film on the end surface of the slab waveguide. 4. A step of transferring a pattern to be a reflection end by exposure on a photoresist coated on a surface of a region of only a clad layer connected to a channel waveguide on a substrate,
A method of manufacturing a light reflecting end, comprising: a step of removing an unnecessary portion of the region by using the pattern as a mask to expose a clad end surface; and a step of forming a light reflecting film on the clad end surface. 5. A reflection-type optical interferometer comprising a combination of a plurality of waveguides with different light-reflecting ends each having a light-reflecting end, and an optical coupler to which these waveguides are connected. An optical interferometer using the reflecting end according to Item 1 or 2. 6. The optical interferometer according to claim 5, wherein a directional coupler is used as the optical coupler. 7. The optical interferometer according to claim 5, wherein a slab waveguide is used as the optical coupler.